1. Field of the Invention
This invention relates generally to a shaker table assembly to which manufactured devices are mounted for vibrational testing and, more particularly, it relates to an interposer device for adjusting and controlling spring constants for the shaker table assembly.
2. Description of the Prior Art
Shaker tables for testing the reliability and durability of manufactured devices are well known in the art. Such shaker tables are used either under controlled laboratory conditions or in conjunction with an assembly line. Often, shaker tables are mounted with thermal chambers, which gives the added flexibility of testing for defects in the manufactured product which can be exposed by elevated temperature or temperature cycling.
The shaker tables typically include a platform or mounting table upon which a device to be tested is mounted. At least one vibrator assembly is typically attached to the mounting table by a piston mounting bolt and vibrates the mounting table thereby vibrating the device mounted upon the mounting table. The vibrator assembly generally consists of a housing having a slidable piston mounted therein. The slidable piston strikes a programmer comprising a shock absorbing material to achieve a predicted predetermined shock response. The programmer is typically press-fit mounted within the housing adjacent the mounting table and typically secured therein by either epoxy or set screws. Unfortunately, upon continual striking of the programmer by the slidable piston of the vibrator assembly of the prior art, the epoxy tended to delaminate from around the programmer and the programmer becomes detached from within the housing and ultimately causes the vibrator assembly to fail.
In order to adjust the predicted predetermined spring constant of the prior art shaker tables between the mounting table and the vibrator assembly, the entire vibrator assembly had to be completely removed from the mounting table and a new vibrator assembly having the necessary predicted predetermined spring constant had to be mounted to the mounting table. Or, the vibrator assembly had to be disassembled and the programmer mounted therein had to be either adjusted or replaced within the vibrator assembly. Needless to say, the entire procedure of changing or adjusting the vibrator assembly to change the predicted predetermined spring constant of the vibrator assembly requires a shaker table user to maintain an inventory of vibrator assemblies having various predicted predetermined spring constants and/or requires unnecessary down time of the shaker table and increased labor table to disassemble the vibrator assembly.
Furthermore, as described in the Hobbs, U.S. Pat. No. 5,589,637, the vibrator assembly of the shaker table assembly was susceptible to damage from "fretting". Fretting occurred due to the fact that the mounting table and the housing are constructed from an aluminum material allowing an aluminum oxide layer to form between the mounting table and the housing of the vibrator assembly. Therefore, titanium spacers were mounted between the housing of the vibrator assembly and the mounting table reducing the occurrence of fretting and providing thermal insulation. The spacers only reduced thermal transfer between the mounting table and the housing of the vibrator assembly thereby reducing the potential for thermal damage of the vibrator assembly. The spacers did not address the need for a means for adjusting and controlling the spring constant of the shaker table assembly.
A need exists for an interchangeable interposer device mountable between a mounting table and a vibrator assembly of a shaker table assembly which controls the spring constant of the shaker table assembly. Furthermore, there exists a need for an interchangeable interposer device mountable between a mounting table and a vibrator assembly of a shaker table assembly which is easily interchangeable without disassembly of the vibrator assembly to adjust the spring constant of the entire shaker table assembly.